Thickness Dependence of Structure and Optical Characteristics in Fluorine-Doped SnO2 Films Grown by Spray Pyrolysis Method

Abstract

Transparent conducting thin films of fluorine-doped SnO2 were deposited on glass substrates by a spray pyrolysis technique in order to investigate the effect of film thickness. These films were prepared at a substrate temperature of 500 °C. The thickness of the samples was between approximately 70 nm and 1.5 µm. The preferred grain orientation of the films varied with increasing film thickness. The grain size of the surface increased with increasing film thickness. Crystal growth occurred at several stages of film growth. In the first stage, pores were formed in the film. Secondly, the grains grew in two dimensions and completely coved the substrate surface. Finally, the grains became columnar crystals with increasing film thickness. The electrical resistivity decreased with increasing film thickness although this was accompanied by a decrease in optical transmittance. The IR absorption increased despite a constant carrier concentration. Film thickness also increased. This result meant that with a constant high carrier concentration, the increased film thickness enhanced the absorption.